Continuously variable traction roller transmission

ABSTRACT

A continuously variable traction roller transmission comprises a pair of eccentric shafts mounted to a pair of roller support members, each being disposed so that a line linking eccentric axes thereof is inclined with respect to the axial direction of a pair of rotation shanks.

BACKGROUND OF THE INVENTION

The present invention relates to a continuously variable traction rollertransmission.

One of previously proposed continuously variable traction rollertransmissions is disclosed, for example, in JP-A 61-124764. Thiscontinuously variable traction roller transmission comprises an inputrotating disc connected to an input shaft, an output rotating discdisposed to face the input rotating disc, a pair of rollers disposed tocontact opposed surfaces of the rotating discs for transmitting rotationof the input rotating disc to the output rotating disc, a pair ofretainers for rotatably supporting the rollers through eccentric shaftseach having a pair of eccentric and parallel rotation shaft portions,and a pair of tie rods for supporting the retainers and guiding movementin the direction of tangent lines of the rotating discs and rotation inthe direction of movement so as to tilt the rollers and change a contactposition thereof with the rotating discs, each tie rod being supportedby a support pin arranged in the opposed direction of the rotating discsto be rotatable about the support pin. Input torque operates to pressdown one of the rollers, and press down the other thereof. The otherroller produces an upward offset. When input torque operates this offsetroller, each eccentric shaft is swung on the rotation shaft portionthereof supported by the retainer which is rotated simultaneously aboutthe tie rod as a support shaft for rotating the roller, thus achievingdecelerating action. Upon deceleration action, the retainer is movedupward by swing of the eccentric shaft. In accordance with upwarddisplacement and rotational displacement of the retainer, a camconnected to the retainer is operated to move a shift control valvethrough the cam. Thus, a hydraulic piston for vertically driving theretainer undergoes hydraulic pressure against upward movement of theretainer. When force due to hydraulic pressure balances with upwardforce of the retainer, an offset of the roller becomes null, so that ashift ceases. Likewise, the one roller produces a downward offset, andcarries out similar deceleration action.

As to the known continuously variable traction roller transmission,however, even if the shift valve does not operate, an increase in inputtorque causes a shift on the deceleration side due to elasticdeformation of a disc, etc. Moreover, the pair of eccentric and parallelrotation shaft portions of the eccentric shaft are disposed to have apositional relationship where the retainer has less upward and downwardmovement due to swing of the eccentric shaft, so that when actuating theshift control valve to produce within the hydraulic piston hydraulicpressure against upward force of the retainer, it is necessary to rotateextra on the deceleration side the cam for feed backing movement of theretainer to the shift control valve, resulting in extra deceleration.Thus, the speed ratio is changed with torque variations, resulting in adifficult logic of shift control, or engine over-rotation.

It is, therefore, an object of the present invention to provide acontinuously variable traction roller transmission which enables areduction in variation of the speed ratio due to torque increase.

SUMMARY OF THE INVENTION

There is provided, according to the present invention, a continuouslyvariable traction roller transmission, comprising:

input and output discs, said input and output discs defining a toroidalconcavity, said input and output discs having axes;

a pair of traction rollers disposed in said toroidal concavity of saidinput and output discs;

a pair of roller support members arranged to rotatably support said pairof traction rollers, each of said pair of roller support members havinga pair of rotation shanks which cross said axes of said input and outputdiscs at right angles, said pair of rotation shanks supporting rotatablyand movably in an axial direction thereof said each of said pair ofroller support members;

a pair of eccentric shafts mounted to said pair of roller supportmembers for supporting said pair of traction rollers, each of said pairof eccentric shafts having eccentric axes, said each of said eccentricshafts being disposed so that in a non-loading state, a line linkingsaid eccentric axes is inclined with respect to said axial direction ofsaid pair of rotation shanks, said line being inclined in such adirection that elastic deformation of said pair of input and outputdiscs and said pair of traction rollers contributes to move said pair ofroller support members to reduce a variation of a speed ratio of saidinput disk to said output disk in accordance with a torque increase; and

a hydraulic cylinder apparatus arranged to drive said pair of rollersupport members in said axial direction of said pair of rotation shanks.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal section showing a continuously variabletraction roller transmission to which the present invention is applied;

FIG. 2 is a fragmentary cross section taken along the line 2--2 in FIG.1;

FIG. 3 is a fragmentary schematic view showing the continuously variabletraction roller transmission upon non-loading; and

FIG. 4 is a view similar to FIG. 3, showing the continuously variabletraction roller transmission upon loading.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a continuously variable traction rollertransmission includes a first continuously variable traction rollertransmission unit 10 and a second continuously variable traction rollertransmission unit 12 disposed in parallel. The first traction rollertransmission unit 10 comprises a first input disc 14, a first outputdisc 16, and a pair of first traction rollers 18 for transmitting torquebetween the two. A contact surface of each of the first input disc 14and the first output disc 16 with each of the first traction rollers 18is formed in a toroid. By changing a contact state of the first tractionrollers 18 with the first input disc 14 and the first output disc 16,the rotational speed ratio of the first input disc 14 to the firstoutput disc 16 can continuously be altered. In a manner similar to thefirst traction roller transmission unit 10, the second traction rollertransmission unit 12 comprises a second input disc 20, a second outputdisc 22, and a pair of second traction rollers 24. However, arrangementof the second input disc 20 and the second output disc 22 is opposite tothe first input disc 14 and the first output disc 16. That is, the firstoutput disc 16 and the second output disc 22 are disposed adjacent toeach other. The first input disc 14 is supported to an input shaft 26 onthe outer periphery thereof through a ball spline 28. A cam flange 30 isarranged to the first input disc 14 on the rear side thereof. The camflange 30 is axially supported to the input shaft 26 by a thrust bearing32. A cam roller 34 is disposed between facing cam surfaces of the camflange 30 and the first input disc 14. The cam surfaces of the camflange 30 and the cam roller 34 have such a shape as to produce forcefor biasing the first input disc 14 toward the first output disc 16 whenthe first input disc 14 and the cam flange 30 make relative rotation.Likewise, the second input disc 20 of the second traction rollertransmission unit 12 is connected to the input shaft 26 through a ballspline 36. The second input disc 20 undergoes force toward the secondoutput disc 22 by a disc spring 40 which in turn undergoes compressiveforce from a loading nut 38 engaged with the input shaft 26. The firstoutput disc 16 of the first traction roller transmission unit 10 and thesecond output disc 22 of the second traction roller transmission unit 12are arranged to be rotatable together with an output shaft 42 which isrotatably supported to the input shaft 26.

Referring to FIG. 2, the first traction roller transmission unit 10comprises a roller support member 50 which is rotatably and verticallymovably supported by spherical bearings 110, 112 to upper and lowerrotation shanks 50a, 50b. The first traction roller 18 is rotatablysupported to the roller support member 50 through an eccentric shaft 46.The first input disc 14 is rotated in the direction of an arrow as shownin FIG. 2, transmitting torque to the first traction roller 18. Thespherical bearing 110 is supported by a link 114 which is in turnsupported by a link post 116 secured to a casing 100. The roller supportmember 50 has an extension shank 50c. concentrically arranged to therotation shank 50b. The extension shank 50c is so constructed as torotate together with the rotation shank 50b. A piston 124 is disposed tothe extension shank 50c on the outer periphery thereof. The piston 124is inserted in a piston insertion bore 304 formed in a main cylinderbody 302a which is mounted to the casing 100 by a bolt 300. Mounted tothe main cylinder body 302a on the under side thereof is an auxiliarycylinder body 302b secured with the main cylinder body 302a by the bolt300 through a separate plate 306. The main cylinder body 302a and theauxiliary cylinder body 302b constitute a cylinder body 302. Thus,hydraulic chambers 128, 130 are formed on the upper and lower sides ofthe piston 124 which is vertically movable by hydraulic pressure appliedthereto. It is to be noted that in FIG. 2, the left hydraulic chambers128', 130' are arranged to be vertically opposite to the right hydraulicchambers 128, 130. The piston 124 and the piston insertion bore 304 ofthe main cylinder bore 320a constitute a hydraulic cylinder apparatus.

A valve body 310 is disposed below the cylinder body 302. The valve body310 comprises a main valve body 310a, and an auxiliary valve body 310bmounted on the upper side thereof through a separate plate 311. A shiftcontrol valve 410 is disposed in the valve body 310. The shift controlvalve 410 comprises a stepper motor 412 rotated in accordance with thespeed ratio as commanded, a spool 414 with a rack having teeth engagedwith a pinion 412a driven by the stepper motor 412 and being axiallymovable by rotation of the stepper motor 412, a spool 416 having one endconnected to the spool 414 with the rack and being axially movabletherewith by rotation of the stepper motor 412, a sleeve 416 disposed tothe spool 416 on the outer periphery thereof, a spring 419 for biasingthe sleeve 418 leftward as viewed in FIG. 2, and a retainer 420 engagedwith the sleeve 418 at the outside end thereof. Hydraulic passages 422,424 are arranged to the valve body 310a. The hydraulic passage 422 isconnected to the hydraulic chamber 128, whereas the hydraulic passage424 is connected to the hydraulic chamber 130. Line pressure of thehydraulic passage 423 serving as a hydraulic source is distributed totile hydraulic passages 422, 424 in accordance with the relativepositional relationship between the spool 416 and the sleeve 418. Thatis, the relationship between a land of the spool 416 and an oil grooveof the sleeve 418 is established so that in the normal state as shown inFIG. 2, hydraulic pressure within the hydraulic passage 422 is equal tothat one within the hydraulic passage 424, whereas when the spool 416 isrelatively moved leftward as viewed in FIG. 2, hydraulic pressure withinthe hydraulic passage 424 is higher than that one within the hydraulicpassage 422, and when the spool 416 is relatively moved rightward asviewed in FIG. 2, hydraulic pressure within the hydraulic passage 424 islower than that one within the hydraulic passage 422. Arranged to theextension shank 50c at the lower end thereof is a cam 320 which isrotatable together therewith. The cam 320 has a bevel with which a link322 is in contact. Thus, with the cam 320 rotated, the link 322 isswung, so that a pointed end thereof can press the retainer 420.

It is to be noted that the fundamental constitution of the secondtraction roller transmission unit 12 is the same as that one of thefirst traction roller transmission unit 10.

Referring to FIG. 3, as described above, the first traction rollers 18,24 are rotatably mounted to the roller support members 50, 52 asindicated by broken lines in FIG. 3 through the eccentric shafts 46, 48,respectively. Each eccentric shaft 46, 48 is mounted so that in anon-loading state, a line B, B' linking two eccentric axes thereof isinclined with respect to the axial direction or a line A, A' of theroller support member 50, 52. The inclined direction of the line B, B'with respect to the line A, A' is such that elastic deformation of thedisc, traction roller, etc. upon torque increase serves to increaseupward movement of the roller support member 50, 52.

Next, operation of this embodiment will be described. Upon non-loading,the first traction roller transmission units 10, 12 are in a state asshown in FIG. 3. From this state, with torque of the input shaft 26increased, the first input disc 14 rotates in following the cam roller34 by operation of the cam flange 30, and generates simultaneouslythrust corresponding to input torque of the input shaft 26. Thus, thefirst input disc 14 has increased force for pressing the first tractionroller 18, so that the first input disc 14, first output disc 16, firsttraction roller 18, etc. make elastic deformation. In this state, powertransmission is carried out from the first input disk 14 to the firstoutput disc 16. The first traction roller 18 is swung on a shaft portionof the eccentric shaft 46 supported by the roller support member 50,i.e, the line B is rotated counterclockwise, urging the roller supportmember 50 upward as viewed in FIG. 3. Referring also to FIG. 4, at thistime, the shaft portion of the eccentric shaft 46 on the side of theroller support member 50 has a center moved upward by a distance "t"from the state as shown in FIG. 3, becoming in a state as shown in FIG.4. That is, the roller support member 50 is urged upward by theeccentric shaft 46 by the distance "t". In FIG. 4, the line designatedas U represents the center line of eccentric shafts 46, 48 uponnon-loading and the line designated as L represents the center line ofeccentric shafts 46, 48 upon loading. Referring also to FIG. 2, rotationof the left roller support member 50' moved upward is input to theretainer 420 of the shift control valve 410 through the cam 320 and thelink 322, so that the retainer 420 is moved rightward as viewed in FIG.2. As a result, hydraulic pressure within the hydraulic passage 424 isincreased, obtaining an increase in hydraulic pressure within thehydraulic chamber 130. Therefore, the roller support member 50 undergoesdownward force which puts the roller support member 50 in an equilibriumstate, ceasing a shift. Reacted force due to the hydraulic cylinderapparatus is increased by a part corresponding to the distance "t" ofthe roller support member 50, putting the roller support member 50 inthe equilibrium state, resulting in a reduced variation of the speedratio due to torque increase.

It is to be noted that operation of the second traction rollertransmission unit 12 is the same as that one of the first tractionroller transmission unit 10.

What is claimed is:
 1. A continuously variable traction rollertransmission, comprising:input and output discs, said input and outputdiscs defining a toroidal concavity, said input and output discs havingaxes; a pair of traction rollers disposed in said toroidal concavity ofsaid input and output discs; a pair of roller support members arrangedto rotatably support said pair of traction rollers, each of said pair ofroller support members having a pair of rotation shanks which cross saidaxes of said input and output discs at right angles, said pair ofrotation shanks supporting rotatably and movably in an axial directionthereof said each of said pair of roller support members; a pair ofeccentric shafts mounted to said pair of roller support members forsupporting said pair of traction rollers, each of said pair of eccentricshafts having eccentric axes; means for setting said each of saideccentric shafts so that in a non-loading state, a line linking saideccentric axes is inclined with respect to said axial direction of saidpair of rotation shanks, said line being inclined in such a directionthat elastic deformation of said pair of input and output discs and saidpair of traction rollers serves to move said pair of roller supportmembers so as to reduce a variation of a speed ration of said input diskto said output disc in accordance with a torque increase; and ahydraulic cylinder apparatus arranged to drive said pair of rollersupport members in said axial direction of said pair of rotation shanks.